An internal combustion engine refers to an engine in which combustion gas itself generated by combustion of fuels directly functions on a piston, a turbine blade, or the like, to convert thermal energy of the fuel into a mechanical work. The internal combustion engine is generally referred to as a reciprocating type engine in which gas mixture of fuel and air is ignited and exploded in a cylinder to move the piston. However, a gas turbine, a jet engine, a rocket, and the like, also correspond to the internal combustion engines.
The internal combustion engine may be classified into a gas engine, a gasoline engine, a petroleum engine, a diesel engine, and the like, according to used fuels. For instance, the petroleum engine, gas engine and the gasoline engine are ignited by an electrical arc by spark plug, and the diesel engine is naturally ignited by spraying the fuel in high temperature and high pressure air. In addition, the internal combustion engine may also include four-stroke and two-stroke cycle types according to stroke operation of the piston.
It has been generally known that the internal combustion engine of the vehicle has thermal efficiency of about 15% to 35%, and even in maximum efficiency of the internal combustion engine, about 60% or greater of the entire thermal energy may be consumed by thermal energy discharged to the outside through wall of the internal combustion engine, exhaust gas, and the like.
Accordingly, when reducing an amount of the thermal energy discharged to the outside through the wall of the internal combustion engine, efficiency of the internal combustion engine may be increased, such that methods of installing thermal insulation materials on the outside of the internal combustion engine, changing materials or portions of a structure of the internal combustion engine, or developing cooling systems of the internal combustion engine have been used.
In particular, when minimizing the discharge of heat generated in the internal combustion engine through the wall of the internal combustion engine to the outside, efficiency of the internal combustion engine and fuel efficiency of a vehicle may be improved. However, research into thermal insulation materials, thermal insulation structures, and the like, which can be maintained in the internal combustion engine under repeated high temperature and high pressure conditions for a long time has not been accomplished significant improvement.
Therefore, development of a novel thermal insulation material having substantially low thermal conductivity and thermal resistance, and being applied to an internal combustion engine to be maintained for a long period of time has been demanded.